The present invention generally relates to the conversion of organic cellulosic material (biomass) into a useful gas-phase fuel. More particularly, this invention relates to a system and process for quasi-continuous conversion of biomass into synthesis gas (syngas) and suitable for use in small- to medium-scale applications, such as agricultural operations (farms), factories which use biomass as a starting material (paper mills, ethanol plants), and other facilities in which conventional syngas-generating apparatuses and processes would not likely be economical practical.
Biomass gasification is a well-known process for producing synthesis gas (syngas), which as also known in the art is a gas mixture containing varying amounts of carbon monoxide (CO) and hydrogen gas (H2). Though having a lower energy density than natural gas, syngas is suitable for use as a fuel source.
Within a biomass gasifier, a carbonaceous material typically undergoes pyrolysis, during which the carbonaceous material is heated to release volatiles and produce char. Combustion then occurs during which the volatiles and char react with oxygen to form carbon dioxide (CO2) according to the reactionC+O2→CO2 
The next process is the gasification process, during which the char reacts with carbon dioxide and steam (H2O) to produce carbon monoxide and hydrogen gas via the reactionC+H2O→H2+COConsequently, the biomass gasification process employs oxygen or air to combust some of the biomass and produce carbon monoxide and energy, the latter of which is utilized to convert the remaining biomass to hydrogen and additional carbon monoxide.
Various types of gasifier designs are known. The most common type of gasifier used in biomass gasification is believed to be an up-draft design (counter-current) design, in which air, oxygen and/or steam flows upward through a permeable bed of biomass and counter-currently to the flow of ash and other byproducts of the reaction. Typical up-draft gasifiers have significant technical shortcomings. First, the introduction of air into the hot gasification chamber partly combusts the biomass, yielding a lower overall heating value compared to pure gasification. Second, if air is used as the gasification agent, nitrogen in the air is a diluent that reduces the energy content per unit volume of the output gas, making the output gas inconvenient for use in gas turbines, for storage, and for subsequent chemical processing. Third, tars and phenolic hydrocarbons produced in an up-draft gasifier require removal to reduce emissions, avoid fouling of a gas turbine, and avoid catalyst poisoning when used to create liquid fuels. The removal equipment adds to system complexity and size, with the result that for economic reasons the gasifier is usually limited to large installations. Because biomass is a low-energy content fuel and is dispersed geographically, a large-scale gasifier requires transport and storage of the biomass, which negatively affects the economic payback for the system.
In view of the above, there is a need for a biomass gasification equipment capable of economically practical use on medium- to small-scale installations, including direct sources of biomass such as agricultural operations (for example, farms), factories in which biomass materials are starting materials and/or byproducts (for example, paper mills, ethanol plants, etc.), sylvans, bioplants, and small towns and villages.